Pulsed laser systems, such as excimer lasers, are well known. FIG. 11 is an end cross sectional view of a laser chamber, generally illustrated as 10, used in a conventional pulsed laser system. The laser chamber 10 includes an electrode structure 22 defining an electrical discharge area 28, a heat exchanger 60, and a blower assembly 70. As is well known by those skilled in the art, the pulsed laser system produces energy pulses from a gas mixture that is between the electrode structure 22. The mixture of gas, which typically includes krypton and fluorine, is maintained at a high pressure (e.g., 3 atm). The electrode structure 22 ionizes the gas mixture to produce a high energy discharge. A life cycle of the gas mixture is measured by the total number of high energy discharges that the gas mixture can produce. Typically the life cycle ranges from about 100 to about 200 million discharges.
The blower assembly 70 plays the important role of circulating the gases in the laser chamber 10 of pulsed laser systems. The circulation of the gases harbors may purposes, among them which include, but are not limited to, maintaining the temperature of the gases at the most efficient level of reaction, maximizing the life cycle of the gases, and facilitating the overall operation of the pulsed laser system. As mentioned above, krypton and fluorine are gases commonly employed by the laser chamber 10. These gases, however, may adversely affect the mechanical operation of the blower assembly 70, as well as the performance of the pulsed laser system. To pose the problem more concretely, by way of example, the blower assembly 70 is generally defined by a mechanical structure which includes a motor coupled to a shaft by a lubricated bearing assembly such as a ball bearing. The shaft rotates a fan for the circulation of the gases. The bearing assembly has conventionally been manufactured from ferrous material such as 440C stainless steel. The use of ferrous metals harbors a variety of problems. First, the gases, i.e., krypton and fluorine, are capable of corroding and etching the structure of the bearing assembly, and therefore, diminishing the mechanical integrity of the bearing assembly. Second, fluorine reacts with iron, forming iron (III) fluoride particles (FeF.sub.3) which contaminate the laser chamber 10. The iron (III) fluoride particles interfere with the ionization of the gases by the electrode structure 22 for the production of the high energy discharges. Third, the production of iron (III) fluoride also catalyses the degradation of the lubricant used with the bearing assembly. More specifically, perfluoropolyalkylether (PFPE) synthetic oils, such as Krytox 143AB, manufactured by E. I. Du Pont Company, are typically used to lubricate the bearing assembly. The iron (III) fluoride, a Lewis acid catalyst, degrades the PFPE fluid at asperity contact temperatures of up to about 350.degree. C. The scheme for the degradation of PFPE through an autocatalytic pathway is illustrated in FIG. 12. R.sub.f and R'.sub.f in FIG. 12 are PFPE end groups of an unspecified length. The degradation causes not only the production of volatile acyl fluoride and ketone compounds but also the reduction of the average molecular weight of the lubricant. The degraded product escapes from the bearing assembly, causing mechanical wear and failure of the bearing assembly.
The contamination of the laser chamber 10 with iron (III) fluoride particles diminishes the performance of the pulsed laser system. The requirement to continually replace or re-passivate the ferrous metal bearing, in order to effectively operate the blower assembly 70, reduces the gas life cycle of the laser chamber 10. As a result, the overall efficiency and production of the pulsed laser system is vitiated.